1. Field of the Invention
The present invention relates to a method and system for maximizing two-dimensional (2-D) cell animation effect by making a character in animation to have cartoon-like motion in three dimensional (3-D) animation production.
2. Description of the Related Art
Two methods have been widely used for producing animations. The first method produces an animation based on a two-dimensional (2-D) cell. The second method produces an animation by producing an animation in three-dimension (3-D) and rendering the produced animation. In the 2-D cell based animation producing method, a key frame is set by selecting key scenes, drawing the selected key frame in a circle on a paper, and transforming it into a cell. After key frames are produced, an inbetweening process is performed to interpose frames between the key frames, thereby producing the entire animation. In the 3-D based animation producing method, a 3-D modeling process is performed to create 3-D models, and a 3-D animation process is performed on the created 3-D model set. Then, the 3-D animation data is rendered to produce a 3-D animation.
Throughout the specification, a character animation denotes an animation including virtual characters that move in scenes. The development of a computer graphic technology makes it possible to produce an animation including virtual characters moving like human, and accordingly, the character animation has come into the spotlight. The character animation also includes a 2-D character animation and a 3-D character animation. The 2-D character animation is produced through the 2-D animation cell based producing method, and the 3-D character animation is produced through the 3-D animation producing method. Hereinafter, a two-dimensional (2-D) character means a character produced through the 2-D animation cell based producing method and a 3-D character denotes a character produced through the 3-D animation producing method.
In the 2-D character animation, 2-D characters are produced to have exaggerated movements although the 2-D character animation is generally simple like a typical cartoon movie or a flash animation on the Internet. On the contrary, a 3-D character in the 3-D character animation is produced to have realistic movement like human. The 3-D character animation is produced by a key frame scheme and a motion capture scheme.
In the key frame scheme, an animation is produced by selecting key frames to produce 2-D or 3-D animation data and performing an inbetweening process to interpose frames between key frames. However, such a key frame scheme requires great efforts and a lot of time to produce because the inbetweening processes are performed for every each joints of characters. Also, the quality thereof depends on the ability of a producer.
The motion capture scheme is a method for producing 3-D character animation data. That is, data is obtained by capturing the movements of real human using optical, mechanical, and magnetic motion capture equipment, and the animation is produced using the obtained data. Since the motion capture method uses the movements of human to produce the animation, characters in the animation have nature movements. However, the motion capture scheme needs a lot of time to process the huge amount of data, and the great effort and a lot of time to modify the obtained data.
Recently, there has been a trend to produce animations like 2-D cell animations although the animations are produced in 3-D. A cartoon rendering method, one of non-photorealistic animation and rendering (NPAR) technologies, provides the similar scene effect of a 2-D cell animation using a 3-D graphics technology. The cartoon rendering method has been widely used for the NPAR technologies. The cartoon rendering method is also used for some video games and movies. However, in order to embody 2-D cell animation effect, several other technologies are required beside the cartoon rendering method. Among the required technologies, one is a technology to make a character to have the cartoon-like movement.
If a cartoon character moves like real human in an animation, viewers may feel that the animation is un-nature. There are two methods introduced for producing characters to have non-realistic movement. In the first method, a key frame is produced in a cartoon style. In this case, great effort is required and the quality of the animation depends on the ability of a producer. In the second method, the cartoon like movement is produced by deforming realistic motion data such as motions captured data. In this case, the ambiguity problem of cartoon like movement is arisen although the amount of processes for producing animation is significantly reduced. In other words, the NPAR technology performs a mapping process to make a 3-D animation to be looked liked a 2-D animation. However, the NPAR technology has a problem that it is difficult to obtain exaggerated movements that the 2-D animation intends for.
In order to produce an animation including objects each having 3-D joints, a bone animation method has been generally used. A bone structure is a hierarchical structure for imitating the human skeletal structure. The born structure includes a plurality of bones. A character mesh is closely cohered on the bones. A method for closely attaching the mesh on the bone is referred as a skinning process, and data generated by the skinning process is skinning data.
In order to produce a 3-D character animation, a character model is firstly produced through a 3-D modeling process, and a bone structure is built for a hierarchical animation like a human skeletal structure. Then, a skinning process is performed to connect the modeling data and the bone structure. As a result, the modeling data moves along the movement of the bone structure. After the skinning process, animation data is produced to be suitable to the bone structure. The animation data is composed of the motion and rotation data of joints like human, and the animation data has data of each joint as much as the running time of the animation data. If the animation data is applied to the character model, a character animation is produced. Then, the character animation is checked, modified, and rendered, thereby producing the animation.
However, it must be considered how much animation is deformed for a character to have a cartoon like movement or what makes a viewer to feel deformed motion closer to a cartoon like motion. It is necessary to add supplementary elements to a motion to make a viewer to feel a 3-D animation closer to a 2-D animation.